Explanation:
If you tried to enter this hall of fog, you would find it
dissipates around you.
The hall is actually an
optical illusion created by
sunlight backscattering off of a cloud passing below the peak of
the mountain from which this picture was taken.
Known as a
fogbow
and similar in some ways to
"the
glory", the phenomenon is sometimes
seen from airplanes.
The ring's center appears near the image bottom where the shadow of the
photographer is visible.
This shadow
would likely change as clouds passed,
creating a faux moving giant known as the
Brocken Spectre.
In
the picture, several concentric rings of the fogbow appear to create
a hall for this
mountain king.
The cause of fogbow
supernumeraries arcs and glories have
only been understood recently and are relatively complex.
Briefly, small droplets of water
reflect,
refract, and
diffract sunlight backwards towards the Sun.
Atmospheric backscattering phenomena have a
counterpart in astronomy, where looking out from planet Earth
in the direction opposite the Sun yields a bright spot called
the gegenschein.

Note: The APOD text was updated for accuracy on 2010 May 9. Tomorrow's picture: visages de Mars